Suction drainage-bone screw

ABSTRACT

The invention relates to a bone screw (10) which can be anchored in the bone in a firm and vacuum-tight manner, and to the use of the same in arthroplastic surgery and as a drug delivery system. The interior of the bone screw (10) has a continous longitudinal bore (15) through which the medullary canal can be evacuated during the application of bone cement. The use of the bone screw renders it possible to fill the spongiosa honeycombs with bone cement without endangering the life of the patient.

This is a division of application Ser. No. 07/541,099, filed Jun. 20,1990, now U.S. Pat. No. 5,047,030.

BACKGROUND OF THE INVENTION

1. Field of the Invention The invention relates to a bone screw whichcan be anchored in the bone in a firm and vacuum-tight manner, and tothe use of the same in a method of applying bone cement and as a drugdelivery system.

2. Description of the Prior Art

In arthroplastic surgery, most implants are inserted in the bony bedusing so-called bone cement. This bone cement is usually made ofpolymethylmethacrylate or related compounds. However, the bone cementcan only penetrate into the honeycombs of the bone marrow if they areclean and free of fat marrow and cell components.

In the prior art one therefore attempted to wash the bony bed and applythe bone cement under pressure. This technique, also called the "bonelavage and high-pressurizing technique", was usually used when applyingbone cement of a low viscosity.

This technique, however, led to a number of incidents which endedfatally. Studies on animals and clinical examinations both showed thatan increase in intramedullary pressure can lead to reflex cardiac arrestand that it is also possible for fatal fat and bone marrow emboli tooccur. Furthermore, this method did not succeed in keeping the bony bedfree of blood. On the contrary, depending on the blood pressure, theblood flowed into the bony bed and mingled with the bone cement, thusgreatly impairing its qualities; this happened every time theintramedullary pressure (IMP) dropped below the blood pressure level.

Attempts have also been made to improve the bone cement used in clinicsvia mechanical stabilization and prepressurization. This improvement canonly be completely successful in the technique of cementing if theachieved material stabilization in the bone cement can be transferred tothe bony bed of the patient without endangering his life.

SUMMARY OF THE INVENTION

It is the primary object of the invention to provide a method ofapplying bone cement in which said bone cement is applied deeply and inan artefact-free manner around the prosthesis without endangering thelife of the patient.

It is another object of the invention to provide a bone screw which canbe firmly anchored in the bone and allows drainage of the medullarycanal whilst the bone cement is being applied.

It is a further object of the invention to provide a bone screw whichcan be used as a drug delivery system.

The invention provides a method for draining the floor and/or roof ofthe anchorage bed which renders the bed free of blood. As known from theASIF (Association for Studying Internal Fixation), conventional bonescrews, the thread of which has been adapted to the individual loadtransmission, can achieve a tight sealing of the bone canal. This can beachieved with both pre-cut threads and tapping screws. The bone screw ofthe invention has an axially continuous longitudinal canal or bore inits interior and is adapted to receive a vacuum line in the appropriatemanner in the vicinity of the screw head. Thus it is possible to suckthe blood and fat out of the bone canal and the area around it throughthe longitudinal canal of the bone screw.

The invention also provides a bone screw which can be anchored in thebone in a firm and vacuum-tight manner and has a continuous longitudinalcanal in its interior.

According to the invention, said bone screw is used for sucking blood,fat or bone marrow out of the bone canal and the area around it,especially when working with bone cement in arthroplastic surgery. Thebone screw of the invention can also be used as a "drug deliverysystem", the active agent preferably being an antibiotic in a carriersubstance or a cytostatic drug. Using two cannulated screws, one fordrainage and one for perfusion, it is possible to perform a drugperfusion technique, for example to locally treat a metastasis in thebone.

The bone screw of the invention renders it possible to fill the bonecanal with bone cement under vacuum. It is absolutely imperative to fillin the spongiosa with bone cement in the areas in which it is under loadin order to reinforce the framework against deformation. The distaldraining and drying of the bony bed and the method of sucking the bonecement deep into the femur allows complete and artefact-free filling ofthe cement around the prosthesis. Once the medullary canal has beenfilled in, the proximal metaphysal spongiosa is drained separately. Dueto its morphology, the spongiosa has to be opened up from the interiorvia drilling canals so that the spongiosa honeycombs can be filled withcement up to the level of the compact substance and thus almostcompletely reinforced against deformation. The bone marrow is preventedfrom being sucked off through the suction syringe of the bone screw by acortico-spongious plug which acts as a filter. The plug is removed anddistally displaced when the medullary canal is opened. By using the bonescrew of the invention with its longitudinal canal, it is possible tofill in the proximal spongiosa honeycombs via opening canals and undermoderate pressure and complete relief of pressure by means of theapplied vacuum. In this case, the absolute pressure applied to themedullary canal is, for instance, 100 to 150 mbar.

Via the vacuum which builds up during draining, the bone cement issucked deep down into the bone canals and contains no air bubbles. Theresult is that the obtained bone bed is made of highly compact material.

The bone screw of the invention preferably exhibits one or severaltransverse canals, preferably two to nine, more preferably four to six,which contact the longitudinal canal, preferably extend in theapproximate radial direction of the screw and open up to the outside.This leads to a further increase in the effect of the partial vacuum,especially if the diameter of the partial canals decreases the greatertheir distance from the tip of the screw.

The thread of the screw is preferably a tapping screw. In the region ofthe first three thread turns, the screw extends conically towards itstip. The first three turns are designed as thread cutters withchip-removal canals and cut the thread in the bone. This leads to aparticularly tight sealing of the bone.

The dimension of the bone screw varies according to its use. When usedas a cannulated bone screw in the greater trochanter and the medullarycanal of the femur, in particular for applying a vacuum to such a bonecement in the bone, the screw preferably has an outer diameter of about5 to 6.5 mm, more preferably 5.8 mm, a core hole diameter of about 4 to5 mm, more preferably 4.5 mm, a thread length of 15 to 25 mm, morepreferably 20 mm, and a pitch (lead) of 1.5 to 2.5 mm, more preferably 2mm. The thread is preferably a breech block thread or a saw-tooththread, the saw teeth of the thread being inclined towards thelongitudinal axis at an angle of preferably about 45°. The diameter ofthe inner longitudinal canal or bore is about 2.5 to 3.5 mm, preferably3 mm.

When the cannulated bone screw is used in infusion, transfusion andperfusion techniques, the diameter of the inner longitudinal canal orbore is preferably about 1 to 3 mm, more preferably between about 1.5and 2.5 mm. Accordingly, the other dimensions of the screw can besmaller than when the screw is used for applying a vacuum to suck bonecement into the bone.

When the cannulated bone screw is used as a drug delivery system, thediameter of the inner longitudinal canal or bore is preferably about 6to 10 mm, more preferably about 8 mm. In this technique, the drugpreferably exhibits a cylindrical shape, and its diameter is adapted tothe diameter of the inner longitudinal canal of the screw with theresult that the drug can be pushed through the canal from the outside tothe inside where it is applied.

The screw preferably exhibits a tubular piece with a length of about 150to 250 mm, preferably about 200 mm, attached to the thread portion,through which piece the inner longitudinal canal of the screw extends. Aremovable handle with which the bone screw can be screwed into the boneis attached to the rear end of the tubular piece by a spring and a setscrew. Furthermore, this site also exhibits a connection piece for avacuum tube which leads to a sterilisable pump.

The screw is preferably made of an extremely pure surgical steel, suchas V4A steel, or of titanium or a titanium alloy.

If the bone screw is to remain in the body, at least part of it,preferably the whole screw, should be made of an absorbable material.This material is preferably a plastic material or a completelyresorbable material. Such materials are, for instance, described inEP-A-86 90 0132. Examples of such materials are polylactide,polyglycolide or another polyamino acid. The material can be made of acomposite of an absorbable matrix and a filler, the filler preferablybeing a sintered hydroxylapatite or tricalciumphosphate or a finelydispersed Ca-phosphate compound.

When used as a drug delivery system, a plug located at the outer side ispreferably used to hermetically seal the longitudinal canal of the screwonce the drug has been inserted.

In order to reduce its weight, the handle is preferably made of Al or anAl alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings and examples illustrate the invention in greaterdetail.

FIG. 1 is a cross section of a first embodiment of the bone screw of theinvention;

FIG. 2 is a partially cut second embodiment of the bone screw of theinvention;

FIG. 3 is the arrangement of a bone screw of the invention for drainingthe medullary canal of the femur;

FIG. 4 is the arrangement of two bone screws of the invention in thegreater trochanter and the medullary canal of the femur; and

FIG. 5 shows a perspective view of the arrangement of two bone screws ofthe invention used for perfusion purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a first simple embodiment of a bone screw 1 of the invention.The screw 1 has an external thread 2 which is designed as a breach blockthread, the foremost edge of the saw teeth being inclined towards thelongitudinal axis of the screw at an angle of about 45°. The interior ofthe screw 1 has a continuous longitudinal canal 3 along with severalradially extending transverse canals 4 which contact the longitudinalcanal 3. It is possible to appropriately connect a vacuum pump via atube in the area around the screw head 5. In order to be able to applythe vacuum in a uniform manner, the diameter of the transverse canalsincreases the greater their distance from the head 5 of the screw wherethe vacuum pump is connected.

The bone screw 10 according to FIG. 2A has a thread portion 12 at itsfront and a tubular piece 14. The total length 1 is about 120 mm, thelength l_(G) about 20 mm. The external diameter d_(a) of the threads isabout 5.8 mm, whereas the core diameter is about 4.5 mm. Through thecomplete length of the bone screw 10 extends a continuous innerlongitudinal canal 15, the diameter d_(i) of which is about 3 mm. Thetip of the thread is designed as a thread cutter. For this purpose, thetip 16 of the thread portion 12 tapers at an angle α of about 5° to 10°,preferably about 7°, and the first three thread turns of the threadportion are designed as cutters. Furthermore, chip-removal canals areprovided. A sleeve 18 with a groove 20 is provided at the rear end ofthe tubular portion 14. A handle (not shown) is mounted onto the sleeve18, which handle is secured via a spring with a set screw which engageswith the groove 20. Furthermore, a connection piece 22 for a vacuum tube(not shown) is provided at the rear end of the bone screw 10, which tubeleads to an evacuatable pump. FIG. 2B shows an enlarged section of thethread portion 12, wherein the threads 13 are designed as saw teeth. Theedges of the teeth are inclined at an angle of approximately 45° and87°, respectively, with regard to the screw axis.

FIG. 3 shows the arrangement of a bone screw 10 of the invention fordraining the medullary canal of the femur. This technique will beexplained in greater detail in the examples. FIG. 3 shows the handle 24at the rear end of the screw, through which handle the screw 10 is to beturned. The vacuum tube 26 which leads to the pump is mounted on theconnection piece 22 at the rear end of the screw 10. FIG. 3 also showsthat the screw 10 is inserted into a cortico-spongious plug 28 in thefemur 30 below a prosthesis 32.

FIG. 4 is a systematic illustration of a cannulated bone screw 1'inserted for the distal draining of the medullary canal of the femur 30and a proximally inserted cannulated bone screw 1 in the greatertrochanter. This technique, too, will be explained in greater detail inthe examples. FIG. 4 shows a cross section of the proximal bone screw 1and a side view of the distal bone screw 1' inserted into acortico-spongious plug 28.

The following examples illustrate the invention.

EXAMPLE 1

In order to demonstrate the manner in which the femur is drained, anexperiment is carried out in which the corroded, soft tissue-free femurand its canal system are welded into a film in such a manner that thearea surrounding the femur can be evacuated. The femur is then filledwith dye, followed by periostally applying a vacuum in the film andnoting the time it takes for the dye to pass out of the medullary canaland into a collecting vessel via a tube. It was shown that within threeseconds the dye is sucked out of the medullary canal only through thecanal systems located along the linea aspera. For the rest of theexperiment it suffices to seal the metaphysial region of the femur andthe linea aspera with a transparent varnish in order to achieve a highvacuum in the medullary canal. A cannulated bone screw is thenanterolaterally inserted into the femur 2 cm beneath the site whichcorresponds to the tip of the implanted metal prosthesis. The process ofevacuation is carried out via the longitudinal canal of the bone screwwith the result that a vacuum with an absolute pressure of about 100 to150 mbar builds up. The femur is then proximally sealed with siliconerubber and the bone cement applied from the proximal direction to thedistal direction. This is followed by the insertion of a plastic replicaof a Meller standard prosthesis, a damp compress being used to preventthe bone cement from being proximally pressed out. In a secondexperiment, drainage is carried out in several femora both distally andproximally at the same time. In this case, the proximal, cannulated bonescrew is laterally inserted at the greater trochanter in the directionof the lesser trochanter. Evacuation is carried out with the sameintensity in both screws. The filling and insertion of the prosthesis iscarried out in the same way.

The results of these experiments show that the distal application ofvacuum leads to a "water-tight" bone cement filling from the region ofthe shaft up to the transition of the metaphysis. However, in the regionin which deep penetration of the bone cement into the spongiosaframework is aimed at, the bone cement does not penetrate further intothe spongiosa framework than it would have done as a result of thepressure exerted by the prosthesis alone without the application of avacuum.

In the last experimental arrangement with the vacuum in the proximalmetaphysis, when the bone cement has been applied, a shunt formationappears in the form of an air canal along the shaft of the prosthesisbetween the proximal and distal vacuum. The greater suction power isfound to be on the distal side. This leads to the conclusion that theproximal, cannulated screw has a substantially smaller suction effect onthe medullary canal than the distal screw which extends directly intothe medullary canal.

EXAMPLE 2

In an experimental arrangement, the decrease in vacuum in the proximalmetaphysis is measured after a vacuum has been distally applied to themedullary canal. Seven surface drilling holes are drilled at each thelesser trochanter, the calcar femoris and the trochanter along thedorsal, medial, foremost and lateral circumference. Measuring probes arepushed through these holes in steps of 5 mm in the direction of themedullary canal. These measurements are carried out independently at allthree levels. Once the measurements have been carried out, the drillingholes are refilled with a plastic material.

These measurements yield interesting and surprising findings. They areextremely informative as regards the application of cement under highpressure, but can be explained by the development and growth pattern ofthe bone.

The proximal metaphysis is characterised by the fact that starting fromthe medullary canal, the vacuum decreases rapidly up to the metaphysialcompacta to a value around atmospheric pressure, i.e. the medullaryspaces of the spongiosa are not drained in the direction of themedullary canal, but in the direction of the periosteum.

The effect of the high vacuum on the coronary circulation is examined inanimal experiments. To begin with, a vacuum of 100 mbar absolutepressure is applied via an opening canal in the patellar groove of oneanimal via a cannulated bone screw which has been inserted in avacuum-tight manner in the bone. The respiratory rate and pulse rate aremonitored. The connections between the honeycombs of the medullary spacebecome more and more narrow towards the medullary canal, and broader andbroader towards the periosteum. The measurements show a typical increasein pressure from the medullary canal towards the compacta.

EXAMPLE 3

In order to examine the cementing technique in the proximal methaphysisof the femur, in a further series of experiments several femora areopened up from the medullary canal by drilling three medial and threemedio-dorsal holes with a 6 mm drill. This is followed by inserting acannulated bone screw into the greater trochanter, which screw extendstowards the lesser trochanter. As in the above examples, a cannulatedbone screw is anterolaterally inserted into the cortical bone 2 cmdistal of the tip of the prosthesis. The distal screw is placed into acortico-spongious plug to ensure that the distal and proximal medullarycanal remain delimited from the screw by means of a spongiosa filter. Asynthetic or manufactured filter or plug may be used instead of thecortico-spongious plug. The bone is filled with Palacos R® bone cementmixed under vacuum. Prior to application, the bone cement and the mixingvessels are cooled to 1° C. The temperature of the mixture when appliedto the femur is between 18° and 22° C. The femur is proximally sealedwith silicone rubber. After having been precompressed or prepressurized,the bone cement is applied to the femur at the beginning of the fourthminute of the mixing phase. The bone cement is sucked deep down into thefemur by the vacuum applied via the distal, cannulated bone screw. Oncethe prosthesis component has been inserted, the distal vacuum lead ispinched off and the vacuum proximally applied. The silicone rubberprevents the bone cement from being pressed out. The vacuum remainseffective in the metaphysis until the bone cement has hardened.

The preparations are sawed open. They reveal that the distal segments ofthe medullary canal of the proximal half of the femur are completelyfilled with bone cement and that the peripheral spongiosa honeycombs aretotally reinforced by bone cement. Proximally the cement has advanced tothe calcar femoris, laterally it has penetrated approximately 4 to 5 mminto the framework of the cancellous bone.

The comparison between filling from the proximal to the distal directionand filling from the distal to the proximal direction using a nozzleshows that only with distal suction and proximal application of the bonecement can the spongiosa honeycombs be filled and the mingling in ofblood be avoided. In the other methods of application, liquid is pushedalong the interface from the distal to the proximal direction, and veryoften, depending on the viscosity of the bone cement, the liquid will bepushed into the cement mass thus causing lamination and the formation ofhaematocysts. This, in turn, greatly decreases the stability of the bonecement.

EXAMPLE 4

The effect of high vacuum on the coronary circulation is examined inanimal experiments. To begin with, a vacuum of 100 mbar absolutepressure is applied via an opening canal in the patellar groove of oneanimal via a cannulated bone screw which has been inserted in avacuum-tight manner in the bone. The respiratory rate and pulsefrequency are monitored.

It can be seen that no blood is sucked out of the canals once a smallamount of the content of the medullary space has been sucked off. Therespiratory rate and pulse frequency remain completely unchanged.

EXAMPLE 5

Further experiments show that centripetal application via the cannulatedbone screw can be used in the treatment of bone affections. It is shownthat over a certain period of time, active agents in a matrix located inthe canals of the screw can achieve extremely high concentrations at thesite of application. As the bone screw seals the bone in a hermeticmanner, the active substance cannot be retrogradely lost. Furthermore,precise insertion of the screw is possible. The bone screw of theinvention can thus also be used as a "drug delivery system".

EXAMPLE 6

The bone screw of the invention can also be used in a highly effectivelocal treatment applied, for instance, in osteomyelitis and bone tumors.The first cannulated screw is used to apply a drug at highconcentrations directly in or next to the site of focal disease, and thesecond cannulated screw is used to suck off the perfusion liquid in thevicinity of the focal disease in order to avoid penetration of the druginto the circulation.

FIG. 5 shows a perspective view of such an arrangement. In FIG. 5, twocannulated screws 10 are arranged closely above and below a metastasis40 in the femur 30. The two screws 10 are preferably inserted indifferent directions, preferably at an angle of 90° to 180° with respectto one another. The perfusion liquid or drug is applied via the lowerbone screw and is sucked through the longitudinal canal of the upperbone screw which is connected to a vacuum line (not shown). The arrow 42shows the flow of the perfusion liquid. Such a perfusion can be appliedfor several days. In order to facilitate its insertion, the tip of thebone screw of the invention can additonally comprise a self-cuttingdrill.

What is claimed is:
 1. A method of establishing therapeuticcommunication with the interior of a bone, the methodcomprising:providing at least one bone screw, each bone screw having afirst end and a second end and a continuous bore establishing acommunication canal between the first and second ends; inserting atleast the first end of each bone screw into the bone such that each bonescrew is firmly anchored in the bone in an essentially vacuum-tightmanner; and delivering substances to or from the interior of the bonethrough the communication canal of each bone screw.
 2. The method ofclaim 1 wherein the step of delivering substances includes the step ofremoving blood, fat and bone marrow from the interior of the bonethrough the communication canal of a first bone screw by suctiondrainage.
 3. The method of claim 1 wherein the step of deliveringsubstances includes the step of sucking gas from the interior of thebone through the communication canal of a first bone screw therebycreating a partial vacuum within the bone to thereby suck bone cementinto the bone during application of the bone cement.
 4. The method ofclaim 1 wherein the step of delivering substances includes the step ofdelivering drugs into the interior of the bone through the communicationcanal of at least one bone screw thereby creating a drug deliverysystem.
 5. The method of claim 1 wherein the step of deliveringsubstances includes the step of delivering drug concentrations in theform of a perfusion liquid into the interior of the bone through thecommunication canal of a first bone screw at or near the site of adisease for locally treating the disease and the step of draining theperfusion liquid from the interior of the bone through the communicationcanal of a second bone screw.